1. Field of the Invention
This invention relates to hydroxyalkyl aryl ethers of di- and polyhydric phenols and phenolic resins as bonding and stiffening agents having improved physical and mechanical properties such as low volatility, reduced fuming in rubber compounding and improved adhesion properties of vulcanizable rubber and rubber composites.
2. Brief Description of the Prior Art
The performance of rubber composites in articles such as tires, belts and hose products depends on the quality of adhesion between the rubber and reinforcing materials as well as on the mechanical properties of the cured rubber matrix in contact with the reinforcing materials.
The conventional method of optimizing the adhesion of the rubber to the reinforcement entails compounding into the rubber before vulcanization a two part adhesive system that includes a methylene donor and a methylene acceptor. The methylene donor generates methylene or methylol groups capable of reacting or cross linking with a methylene acceptor which interacts with the rubber and reinforcing material with a resultant increase in adhesion of the rubber to the reinforcing material. Because the methylene donor and the methylene acceptor are compounded into the rubber, they have a significant effect on the properties of the final reinforced rubber product.
Dihydric phenols, such as for example resorcinol, polyhydric phenols, such as for example thio-bisphenols including thio-bis-resorcinol or thio-bis-4,4'-diphenol, and phenolic resins, such as for example resorcinol formaldehyde novolak resins, phenol formaldehyde novolak resins and phenol resorcinol formaldehyde novolak resins have long been used in the rubber industry as methylene acceptors. Although these methylene acceptors increase the adhesion of the rubber to the reinforcing materials, they have drawbacks, for example, resorcinolic methylene acceptors can present processing problems by producing volatiles such as resorcinol at Banbury temperatures.
The most commonly used methylene donors are, such as for example, hexamethylenetetramine and various methylol or methoxymethyl melamines. Many other methylene donors are set forth in U.S. Pat. No. 3,751,331.
The in situ resin formed by the reaction of the methylene acceptor and the methylene donor promotes adhesion between the rubber and reinforcing materials such as, for example steel, glass and organic or inorganic filaments, fibers, cords and fabrics, and provides improved rubber vulcanizate properties such as hardness and dynamic stiffness. These compounding additives also act as thermosetting or vulcanizing plasticizers providing easier processability and as excellent extrusions for the rubber compounds. The disadvantage, however, of many of these compounding additives such as, for example, resorcinol is that they generate an undesirable amount of fuming in Banbury mixing and calendering operations.
U.S. Pat. No. 4,889,891 discloses alkyl substituted resorcinolic novolak resins as suitable methylene acceptors for vulcanizable rubber compositions.
U.S. Pat. No. 4,892,908 discloses the use of keto derivatives of resorcinol such as, for example, benzoyl resorcinol.
U.S. Pat. No. 4,605,696 discloses monoesters of resorcinol including resorcinol monobenzoate and resorcinol monorosinate.
U.S. Pat. No. 5,021,522 discloses aralkyl substituted resorcinolic novolak resins such as, for example, a styrene substituted resorcinol formaldehyde resin.
U.S. Pat. No. 5,030,692 discloses alkylphenol modified resorcinolic novolak resins.
In spite of these prior art disclosures, there remains a very real and substantial need for the further improved bonding additive hydroxyalkyl aryl ethers of di-and polyhydric phenols and phenolic resins of this invention that may be used as methylene acceptors, which in combination with suitable methylene donors, have enhanced curing properties, and mechanical properties, and that function as improved bonding and stiffening agents in vulcanizable rubber compositions.